Composite material with improved properties

ABSTRACT

A polyolefin resin composition comprising a polyolefin modified with an unsaturated carboxylic acid, at least one member selected from the group consisting of polyepoxides, polyisocyanates, and polyamines, and a reinforcement.

FIELD OF THE INVENTION

The present invention relates to a composite material with improvedproperties which can provide a molded product having excellent variousproperties.

BACKGROUND OF THE INVENTION

Thermoplastic composite materials have excellent mechanical andelectrical properties, and investigations for use as industrialmaterials have recently been developed rapidly. Of polymers constitutingthe composite materials, polyolefins such as polyethylene,polypropylene, and so forth have characteristics such as small specificgravity, good moldability and processability, excellent chemicalresistance, and so forth, and applications of the thermoplasticcomposite materials comprising polyolefins as a matrix will nowincrease.

However, since polyolefins constituting the thermoplastic compositematerials are nonpolar polymers, they do not have a satisfactoryaffinity for glass fibers, carbon fibers, carbon black, mica, talc,alumina fibers, silicon carbide fibers, aromatic polyamide fibers, andso forth which are used as a reinforcement. Therefore, a thermoplasticcomposite material having a further improved reinforcing effect has beendemanded.

Many investigations have been made to develop a thermoplastic compositematerial satisfying the above requirement.

For example, Japanese patent application (OPI) No. 74649/1977 (the term"OPI" as used herein refers to a "published unexamined Japanese patentapplication") describes a material prepared by adding 0.2 to 2 wt% ofpolyacrylic acid to a composite material composed of 50 to 95 parts byweight of a polyolefin and 5 to 50 parts by weight of an inorganicfiller. However, this composite material cannot be said to possesssufficiently improved properties because the affinity of the matrixpolymer for the filler has not yet been improved. Japanese patentapplication (OPI) No. 50041/1980 and U.S. Pat. No. 3,862,265 describe acomposite material composed of a graft polyolefin and an inorganicfiller which is obtained by blending an unsaturated carboxylic acid, apolyolefin, and an inorganic filler, followed by subjecting the blend toa reaction under heating and mixing in an extruder. This compositematerial has good affinity of the graft polyolefin for the inorganicfiller but has not a sufficient flowability since it contains inorganicfibers. Therefore, a molded product prepared from this compositematerial has not a sufficient impact strength. Thus, composite materialshaving improved properties are strongly desired.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide athermoplastic composite material which can provide a molded producthaving excellent mechanical properties (particularly, impact strength),a small specific gravity and a good water repellency.

Another object of the present invention is to provide a compositematerial having a good moldability due to its excellent flowability.

The composite material of the present invention comprises a modifiedpolyolefin (i.e., a polyolefin modified with an unsaturated carboxylicacid), a reinforcement, and at least one polyfunctional compoundselected from the group consisting of a polyfunctional epoxide, apolyfunctional amino compound, and a polyfunctional polyisocyanatecompound.

DETAILED DESCRIPTION OF THE INVENTION

The modified polyolefin used in the present invention can be obtained bygraft-polymerizing an unsaturated carboxylic acid onto a polyolefin andhas an excellent affinity for reinforcements as compared with unmodifiedpolyolefins.

Examples of polyolefins used for preparation of the modified polyolefininclude polyethylene, polypropylene, poly(4-methylpentene-1),ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer,ethylene/propylene/diene copolymer, and so forth. When polypropylene isused, a composite material having particularly various excellentcharacteristics can be prepared.

The modifier used for preparation of the modified polyolefin isunsaturated carboxylic acids and examples thereof include acrylic acid,methacrylic acid, itaconic acid, maleic acid, and anhydrides of theseacids. The amount of these modifiers used is 0.05 to 0.8 part by weight,preferably 0.1 to 0.6 part by weight, per 100 parts by weight of thepolyolefin.

A modified polyolefin prepared using a small amount of the modifier hasnot a sufficient affinity for the reinforcement, making it difficult toprepare a composite material having excellent properties. On the otherhand, when a modified polyolefin is prepared using a large amount of themodifier, modification of the polyolefin does not proceed sufficiently,and a modified polyolefin contains a large amount of unreacted modifier.Such a product tends to deteriorate with the passage of time.

The modified polyolefin can be prepared by mixing a polyolefin, amodifier, and a catalyst in predetermined proportions and reacting theresulting mixture at 150° to 280° C. for 1 to 20 minutes. When thereaction temperature and/or the reaction time exceed(s) theabove-described range(s), the modified polyolefin obtained showsunfavorable coloring or unnecessary thermal decomposition.

Examples of the catalysts used for the preparation of the modifiedpolyolefin include benzoyl peroxide, lauroyl peroxide, and ketal ordialkyl peroxides which have a decomposition temperature necessary forattaining the half life of 10 hours of at least 80° C. Specific examplesof the ketal or dialkyl peroxide catalysts include1,1-bis(t-butylperoxy)cyclohexane, n-butyl4,4-bis(t-butylperoxy)valerate,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane, dicumylperoxide, t-butylcumyl peroxide,α,α'-bis(t-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.

When the modified polyolefin is prepared using ketal peroxides ordialkyl peroxides having a decomposition temperature necessary forattaining the half life of 10 hours of at least 80° C., it exhibits amore effective molecular weight-lowering effect as compared with themodified polyolefin prepared using other catalysts. Accordingly, thecomposite material of the present invention prepared using the modifiedpolyolefin has excellent moldability. Further, in crystallization of thepolymer in the process for molding of the composite material of thepresent invention, the modified polyolefin prepared by using thespecified ketal peroxides or dialkyl peroxides and benzoyl peroxide in aweight ratio of 10/1 to 1/10, preferably 1/6 to 6/1, exhibits an effectof inhibiting the growth of spherulites and, as a result, a compositematerial having good characteristics (a spherulite size of 50μ or less,preferably 5 to 30μ) can be obtained.

The amount of the catalyst used is 0.03 to 3 parts by weight, preferably0.05 to 1 part by weight, per 100 parts by weight of the polyolefin.

As a modification reaction of the polyolefins, a solution reactionprocess using a solvent as a reaction medium or a method in which thereaction is conducted in a heat-melting state can be employed. From thestandpoint of prevention of unnecessary coloring of the modifiedpolyolefin obtained, prevention of unnecessary lowering of the molecularweight of the polyolefin, and the choice of an appropriate reactiontime, it is preferred to employ a heat-melting reaction using anextruder as a reactor.

Polyfunctional epoxy compounds used in the present invention arecompounds having two or more epoxy groups in the molecule. Examplesthereof include a bisphenol A type epoxy compound, a bisphenol F typeepoxy compound, an aliphatic ether type epoxy compound, a novolak typeepoxide, an isocyanurate type epoxide and so forth. Specific examplesthereof include condensates between bisphenol A and epichlorohydrin;polyglycidyl ethers of polyols such as ethylene glycol, propyleneglycol, polyethylene glycol, glycerol, neopentyl glycol,trimethylolpropane, and sorbitol; triglycidyl isocyanurate,N-methyl-N',N"-diglycidyl isocyanurate, and triglycidyl cyanurate. Themolecular weight of these polyfunctional epoxides is, though notparticularly limited, about 4,000 or less.

Polyfunctional amines used in the present invention are compounds havingtwo or more amino groups in the molecule. Specific examples thereofinclude hexamethylenediamine, tetramethylenediamine, methaxylenediamine,diaminodiphenylmethane, diaminodiphenyl sulfone, 3,3'-diaminobenzidine,isophthalic acid hydrazide, diaminodiphenyl ether, nanomethylenediamine,and diethylenetetramine.

Polyfunctional isocyanates are compounds having two or more isocyanategroups in the molecule. Examples thereof include tetramethylenediisocyanate, toluidine diisocyanate, diphenylmethane diisocyanate,naphthalene diisocyanate, and their polyisocyanates obtained byextending them with a chain-extending agent. Of these polyfunctionalcompounds, polyepoxides having a cyanuric or isocyanuric ring have highreactivity toward the modified polyolefin in the process of preparingthe composite material of the present invention and a molding productprepared from the composite material thus-obtained has more excellentimpact strength as compared with other molded products.

Polyfunctional epoxides, polyfunctional amines, and polyfunctionalisocyanates can be used alone or in combination, the amount thereof iseach 0.03 to 5 wt% per the weight of the modified polyolefin but thetotal amount does not exceed 10 wt% per the weight of the modifiedpolyolefin.

Molded products prepared from the composite material containing at leastone of those polyfunctional amines, polyfunctional isocyanates, andpolyfunctional epoxides of the present invention have an excellentstrength characteristic as compared with molded products prepared fromcomposite materials containing no those polyfunctional compounds.

Reinforcements used in the present invention are fibrous materials suchas glass fibers, carbon fibers, graphite fibers, aromatic polyamidefibers, silicon carbide fibers, polysulfone type fibers, polyetherketone fibers, alumina fibers, potassium titanate fibers, asbestosfibers, boron fibers, metal fibers, and so forth. Fibers having thelength of 5 mm or less, preferably 0.01 to 3 mm, are preferred.

As other reinforcements, powdery or flaky materials such as glassflakes, talc, mica, kaolin, clay, diatomaceous earth, calcium carbonate,calcium sulfate, magnesium oxide, carbon black, titanium oxide, metalpowders, alumina, graphite, white carbon, wollastonite, molybdenumdisulfide, and tungsten disulfide can be used. Those reinforcements areincorporated in the modified polyolefin alone or in combination thereofin an amount of 5 to 80 wt% per the weight of the modified polyolefin.If the amount of the reinforcement is too small, a sufficientreinforcing effect cannot be obtained. On the other hand, if the amountof the reinforcement is too large, moldability of the composite materialis reduced and the mechanical properties of a molded product preparedfrom the composite material tend to deteriorate.

Other thermoplastic plastics, for example, engineering plastics such aspolyamides, unmodified polyolefins, polyesters, polycarbonates,polyacetals, and polysulfones can be incorporated into the compositematerial of the present invention, if desired.

The composite material of the present invention is prepared by blendinga modified polyolefin, at least one compound selected from the groupconsisting of polyfunctional epoxides, polyfunctional amines, andpolyfunctional isocyanates, and a reinforcement in the predeterminedproportions. This composite material can be molded into the desiredmolded product by an injection molding method or the like.

Moldability of the composite material of the present invention issuperior to that of similar kinds of conventional composite materials.Thus, it is believed that a molded product prepared from the compositematerial of the present invention has sufficiently improved impactstrength as compared with that prepared from similar kinds ofconventional composite materials.

The present invention will now be explained in detail by reference tothe following non-limiting examples. Unless otherwise indicated, allpercents, parts, ratios and the like are by weight.

EXAMPLE 1

To 100 parts by weight of polypropylene powders having an inherentviscosity of 1.5 (measured in a tetralin solution at 135° C.) were addedmodifiers and peroxides with the amounts as shown in Table 1, and themixture was blended in the Henschel mixer. The mixture was then fed intoan extruder reactor of 30 φ and L/D=25, and modified in a mixed stateunder heat-melting at a reaction temperature of 230° C. for a reactiontime of 7 minutes. The unreacted modifier was removed by reducing thepressure of the vent portion of the extruder, and then the reactionmixture was extruded into pellets to give modified polyolefins.

To 100 parts by weight of the resulting modified polyolefin pellets wereeach added prescribed amounts of reinforcements and polyfunctionalcompounds as shown in Table 1. The mixture was blended in a tumbler andmelt mixed in an extruder, and extruded therefrom to give pellets ofcomposite materials.

These composite materials were formed into 3 kinds of molded products,viz., plates of No. 1 dumbbell, 125×12.5×3.2 (mm), and 125×12.5×6.4 (mm)using a screw on-line type injection machine under molding conditions ofa cylinder temperature of 220° C. and a mold temperature of 60° C.

The results obtained by measuring fabrication properties of thecomposite materials and mechanical properties of the molded productstherefrom under the following conditions are shown in Table 1.

Melt Flow Index (molding flow index):

ASTM-D-1238, load 2.16 kg, temperature 230° C.

Izod Impact Strength: ASTM-D-256

Heat Distortion Temperature (hereinafter referred to as HDT): ASTM-D-648##EQU1##

    TABLE 1      Experiment No.  1 2 3 4 5 6 7 8 9 10 11 12       Composition of composite material Polypropylene 100 100 100 100 100     100 100 100 100 100 100 100 Parts by weight Peroxide Kind -- Benzoyl --     Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl      peroxide  peroxide peroxide peroxide peroxide peroxide peroxide     peroxide peroxide peroxide Parts by weight -- 0.3 -- 0.3 0.3 0.3 0.3 1.0     0.3 1.0 0.3 0.3 Modifier Kind -- Maleic -- Maleic Maleic Maleic Acrylic     Acrylic Acrylic Acrylic Maleic Maleic   anhydride  anhydride anhydride     anhydride acid acid acid acid anhydride anhydride Parts by weight -- 0.3     -- 0.3 0.3 0.3 0.3 0.7 0.3 0.7 0.3 0.3 Polyfunctional compound Kind --     -- Hexa- Hexa- Hexa- -- -- -- Hexa- Hexa- 2,4- 4,4'-    methylene     methylene methylene diamino   methylene methylene Toluilene Diphenyl-     diamine diamine diamine diphenyl   diamine diaminediisocyanate methane         ether      diisocyanate Parts by weight -- -- 0.3 0.3 3.0 0.5 -- --     0.3 0.3 0.3 0.3 Reinforcement Kind Carbon Carbon Carbon Carbon Carbon     Carbon Carbon Carbon Carbon Carbon Carbon fiber Carbon fiber  fiber     fiber fiber fiber fiber fiber fiber fiber fiber fiber Parts by weight 25     25 25 25 25 25 25 25 25 25 25 25 Mechanical property of molded product     Flexial strength 770 1,140 820 1,470 1,540 1,460 1,160 1,230 1,460 1,570     1,530 1,550 (kg/cm.sup.2) Flexial modulus 8.8 8.8 8.8 8.8 8.7 8.7 8.6     8.6 8.7 8.8 8.4 8.6 (× 10.sup.4 kg/cm.sup.2) Izod impact strength     15 18 16 31 33 28 17 19 29 27 34 33 (kg-cm/cm.sup.2) HDT (°C.)     145 148 145 147 143 145 148 147 147 149 146 145 Ratio of improvement in     1.0 1.5 1.1 1.9 2.0 1.9 1.5 1.6 1.9 2.0 2.0 2.0 strength (ratio) Remark     Comparative " " Invention Invention Invention Comparative Comparative     Invention Invention Invention Invention  Example      Example Example     MFI Spherical size (μ) Moldability into flat plate 1 mm thick       Experiment No.  13 15 16 17 18 19 20 21 22 23 24       Composition of composite material Polypropylene 100 100 100 100 100     100 100 100 100 100 100 Parts by weight Peroxide Kind Benzoyl Benzoyl     Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl Benzoyl -- Benzoyl Benzoyl     peroxide  peroxide peroxide peroxide peroxide peroxide peroxide peroxide     peroxide  peroxide Parts by weight 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 --     0.3 0.3 Modifier Kind Maleic Maleic Maleic Maleic Maleic Maleic Acrylic     Acrylic -- Maleic Maleic anhydride  anhydride anhydride anhydride     anhydride anhydride anhydride acid acid  anhydride Parts by weight 0.3     0.3 0.3 0.3 0.3 0.3 0.3 0.3 -- 0.3 0.3 Polyfunctional compound Kind     Triglycidyl Bisphenol A Neopentyl- -- Triglycidyl Hexamethylene Hexamethy     lene Triglycidyl -- -- 4,4-Diphenyl-  isocyanurate diglycidyl glycol di-      isocyanurate diamine diamine isocyanurate   methylene   ether glycidyl           diisocyanate    ether Parts by weight 0.3 0.3 0.3 -- 0.3 0.3 0.3     0.3 -- --  0.5 Reinforcement Kind Carbon fiber Carbon Carbon Glass Glass     fiber Glass fiber Glass fiber Carbon Talc Talc Talc   fiber fiber fiber       fiber Parts by weight 25 25 25 25 25 25 25 25 25 25 25 Mechanical     property of molded product Flexial strength 1,580 1,460 1,500 1,080     1,330 1,280 1,250 1,600 430 500 560 (kg/cm.sup.2) Flexial modulus 8.9     8.6 8.7 5.3 5.5 5.4 5.3 8.5 4.3 4.3 4.3 (× 10.sup.4 kg/cm.sup.2)     Izod impact strength 32 28 30 20 25 27 28 30 10 10 19 (kg-cm/cm.sup.2)     HDT (°C.) 151 150 151 145 144 145 148 149 80 80 82 Ratio of     improvement in 2.1 1.9 1.9 1.2 1.5 1.5 1.4 2.1 1.0 1.0 1.3 strength     (ratio) Remark Invention Invention Invention Comparative Invention     Invention Invention Invention Comparative Comparative Invention     Example     Example Example MFI Spherical size (μ) Moldability into     flat plate 1 mm thick       Experiment No.  25 26 27 28 29 30 31 32 33 34 35       Composition of composite material Polypropylene 100 100 100 100 100     100 100 100 100 100 100 Parts by weight Peroxide Kind Benzoyl Benzoyl     Benzoyl Benzoyl 1,1-Bis(t- 2,5-Dimethyl- Benzoyl *1 *2 *2 --  peroxide     peroxide peroxide peroxide butylperoxy)- 2,5-di(t- peroxide      3,3,5-     butylperoxy)-      trimethyl- hexyne-3      cyclohexane Parts by weight     0.3 0.3 0.3 0.7 0.2 0.2 0. 0.2 0.2 0.2 -- Modifier Kind Maleic Maleic     Maleic Maleic Maleic Maleic Maleic Maleic Maleic Maleic --  anhydride     anhydride anhydride anhydride anhydride anhydride anhydride anhydride     anhydride anhydride Parts by weight 0.3 0.3 0.3 0.7 0.3 0.3 0.3 0.3 0.3     0.3 -- Polyfunctional compound Kind triglycidyl Triglycidyl Triglycidyl     Triglycidyl Triglyjcidyl Triglycidyl Triglycidyl Triglycidyl Triglycidyl     Triglycidyl Triglycidyl  isocyanurate isocyanurate isocyanurate isocyanur     ate isocyanurate isocyanurate isocyanurate isocyanurate isocyanurate     isocyanurte isocyanurate Parts by weight 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3     0.3 0.3 0.3 Reinforcement Kind Talc Glass fiber Talc/carbon Carbon fiber     Carbon fiber Carbon fiber Carbon fiber Carbon fiber Carbon fiber Carbon     fiber Carbon fiber    fiber = 1/1 Parts by weight 25 25 50 25 25 25 25     25 25 25 25 Mechanical property of molded product Flexial strength 540     1,320 1,530 1,640 1,480 1,450 770 1,500 1,560 1,470 750 (kg/cm.sup.2)     Flexial modulus 4.5 5.4 10.1 8.2 8.7 8.7 8.4 8.6 8.7 8.6 8.3 (×     10.sup.4 kg/cm.sup.2) Izod impact strength 17 27 29 32 29 20 11 35 33 17     13 (kg-cm/cm.sup.2) HDT (°C.) 80 148 149 149 144 146 141 148 149     145 141 Ratio of improvement in 1.3 1.5 2.0 2.1 1.9 1.4 1.0 1.9 2.0 1.9     1.0 strength (ratio) Remark Invention Invention Invention Invention     Invention Invention Comparative Invention Invention Invention Comparative             Example    Example MFI      39.9 6.1    5.6 Spherical size     (μ)     100 100 100 10 10 100 100 Moldability into flat     Better     Best Bad Better Better Better Bad plate 1 mm thick       Experiment No.  36 37 38 39 40 41       Composition of composite material Polypropylene 100 100 100 100 100     100 Parts by weight Peroxide Kind Benzoyl Benzoyl Benzoyl *1 *1 *1     peroxide peroxide peroxide Parts by weight 0.2 0.2 0.2 0.2 0.2 0.2     Modifier Kind Maleic Maleic Maleic Maleic Maleic Maleic  anhydride     anhydride anhydride anhydride anhydride anhydride Parts by weight 0.3     0.3 0.3 0.3 0.3 0.3 Polyfunctional compound Kind Triglycidyl Hexa-     Bisphenol A Triglycidyl Hexamethylene Bisphenol A  isocyanurate methylene      diglycidyl isocyanurate diamine diglycidyl   diamine ether   ether     Parts by weight 0.6 0.6 0.6 0.6 0.6 0.6 Reinforcement Kind Carbon fiber     Carbon Carbon Carbon fiber Carbon fiber Carbon   fiber fiber   fiber     Parts by weight 25 25 25 25 25 25 Mechanical property of molded product     Flexial strength 1,750 1,520 1,510 1,700 1,480 1,470 (kg/cm.sup.2)     Flexial modulus 8.6 8.5 8.7 8.7 8.6 8.6 (× 10.sup.4 kg/cm.sup.2)     Izod impact strength 40 33 30 38 30 29 (kg-cm/cm.sup.2) HDT (°C.)     145 144 146 146 145 146 Ratio of improvement in 2.3 2.0 2.0 2.2 1.9 1.9     strength (ratio) Remark Invention Inven- Invention Invention Invention     Invention   tion MFI Spherical size (μ) 10 10 10 10 10 10 Moldability     into flat Good Good Good Best Best Best plate 1 mm thick     Notes     *1: A mixture of benzoyl peroxide and     1,1bis(t-butylperoxy)-3,3,5-trimethylcyclohexane (1:1)     *2: A mixture of benzoyl peroxide and     2,5dimethyl-2,5-di(t-butylperoxy)hexyne-3 (1:1)

EXAMPLE 2

To 100 parts by weight of polypropylene powders having an inherentviscosity of 2.0 (measured in a tetralin solution of 135° C.) were eachadded peroxides as shown in Table 2 and 0.3 part of maleic anhydride asa modifier, and the mixture was blended uniformly in the Henschel mixer.The mixture was then subjected to a heat-melting reaction underconditions of a reaction temperature of 250° C. and a reaction timeperiod of 7 minutes.

The results obtained by measuring the inherent viscosity of modifiedpolypropylenes thus-obtained are shown in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                     Inherent Viscosity                                                            Amount of Peroxide Added (parts)                                 Peroxide       0      0.05   0.1  0.3  0.4  0.8                               ______________________________________                                        Benzoyl peroxide                                                                             1.75   1.73   1.70 1.62 1.6  1.56                              1,1-Bis(t-butylperoxy)-                                                                      1.75   1.45   1.3  1.00 0.95 --                                3,3,5-trimethyl                                                               cyclohexane                                                                   Dicumyl peroxide                                                                             1.75   1.08   1.32 1.08 0.98 --                                Benzoyl peroxide/1,1-                                                                        1.75   --     1.31 1.09 --   --                                Bis(t-butylperoxy)-3,3,5-                                                     trimethyl cyclohexane                                                         (1:1 weight ratio mixture)                                                    ______________________________________                                    

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A polyolefin resin composition comprising:(a) a polyolefin selected from the group consisting of polyethylene, polypropylene, poly(4-methylpentene-1), ethylene/vinyl acetate copolymer, ethylene/ethylacrylate copolymer, and ethylene/propylene/diene copolymer modified with from 0.05 to 0.8 parts by weight per 100 parts by weight of the polyolefin, of a grafted unsaturated carboxylic acid; (b) no more than 10 weight %, based on the weight of said modified polyolefin, of a polyfunctional epoxide, polyfunctional amine, polyfunctional isocyanate or mixtures thereof with the proviso that the amount of any given polyfunctional agent is within the range of 0.03 to 5 weight %; and (c) from 5 to 80 weight % of a reinforcing material, based on the weight of the modified polyolefin of(i) a fibrous material selected from the group consisting of glass fibers, carbon fibers, graphite fibers, aromatic polyamide fibers, silicon carbide fibers, polysulfone fibers, polyether ketone fibers, alumina fibers, potassium titanate fibers, asbestos fibers, boron fibers or metal fibers; or (ii) powdery or flaky materials selected from the group consisting of glass flakes, talc, mica, kaolin, clay, diatomaceous earth, calcium carbonate, calcium sulfate, magnesium oxide, carbon black, titanium oxide, powdered metal, alumina, graphite, white carbon, wollastonite, molybdenum disulfide and tungsten disulfide.
 2. The composition of claim 1, wherein the modified polyolefin is prepared by reacting a polyolefin and said unsaturated carboxylic acid in the presence of at least one catalyst selected from the group consisting of ketal peroxides and dialkyl peroxides which have a decomposition temperature necessary for attaining the half life of 10 hours and at least 80° C.
 3. The composition of claim 1, wherein the modified polyolefin is prepared by reacting a polyolefin and said unsaturated carboxylic acid in the presence of a mixed catalyst system comprising at least one member selected from the group consisting of ketal peroxides and dialkyl peroxides which have a decomposition temperature necessary for obtaining the half life of 10 hours at at least 80° C., and benzoyl peroxide.
 4. The polyolefin resin composition of claim 3, wherein the weight ratio of said at least one member selected from the group consisting of ketal peroxides and dialkyl peroxides to benzoyl peroxide in the mixed catalyst system is 1/10 to 1/1.
 5. The polyolefin resin composition of claim 1, wherein the modified polyolefin is prepared by heat-melting the unsaturated carboxylic acid, the polyolefin, and the polyfunctional compound in the presence of a peroxide type catalyst.
 6. The composition of claim 5, wherein the modified polyolefin is prepared by extruding the reactants which form the same from an extruder type reactor.
 7. The polyolefin resin composition of claim 2, wherein the ketal or dialkyl peroxide catalyst is at least one member selected from the group consisting of 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl 4,4-bis(t-butylperoxy)valerate, 2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α,α'-bis(t-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
 8. The composition of claim 3, wherein the modified polyolefin is in the form of spherulites of a size of 50μ or less.
 9. The composition of claim 1, wherein the polyfunctional compound is a polyepoxide having an isocyanurate or cyanurate ring.
 10. The composition of claim 1, wherein the reinforcing material is carbon fiber.
 11. The composition of claim 1, wherein the improvement ratio of the strength of a molded product prepared from a composition consisting of the modified polyolefin and said reinforcing material to that of a molded product prepared from a polyolefin resin composition consisting of an unmodified polyolefin and said reinforcing material is at least 1.5.
 12. The composition of claim 1, wherein said polyfunctional epoxide is a bisphenol A epoxy compound, a bisphenol F epoxy compound, an aliphatic ether epoxy compound, a novolak epoxide or an isocyanurate epoxide.
 13. The composition of claim 1, wherein said polyfunctional amine is hexamethylene diamine, tetramethylene diamine, methaxylene diamine, diamino diphenylmethane, diaminodiphenyl sulfone, 3,3'-diaminobenzidine, isophthalic acid hydrazide, diamino diphenyl ether, nanomethylenediamine or diethylenetetramine.
 14. The composition of claim 1, wherein said polyfunctional isocyanate is tetramethylene diisocyanate, toluidine diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate or a polyisocyanate obtained by extending a diisocyanate compound with a chain extending agent.
 15. A polyolefin resin composition comprising:(a) a polyolefin selected from the group consisting of polyethylene, polypropylene, poly(4-methylpentene-1), ethylene/vinyl acetate copolymer, ethylene/ethylacrylate copolymer, and ethylene/propylene/diene copolymer modified with from 0.05 to 0.8 parts by weight per 100 parts by weight of the polyolefin, of a grafted unsaturated carboxylic acid; (b) no more than 10 weight %, based on the weight of said modified polyolefin, of a polyfunctional epoxide, polyfunctional amine, polyfunctional isocyanate or mixtures thereof with the proviso that the amount of any given polyfunctional agent is within the range of 0.03 to 5 weight %; and (c) from 5 to 80 weight % of a reinforcing material, based on the weight of the modified polyolefin, of(i) an inorganic fiber, or (ii) at least one member selected from the group consisting of glass flakes, talc, calcium carbonate, magnesium oxide, clay, mica and carbon black, or (iii) an aromatic polyamide fiber. 